Before the board exam, you have to keep complete information about your syllabus, you can get the information about the syllabus from the official website of the school or CBSE/State Board.
Many people trust institute/coaching more than themselves and it is absolutely wrong to think that you can top without institute/coaching.
NCERT Books should always be your first choice, I am saying this for those children who spend more time on any other reference book than NCERT.
Finish Syllabus As Soon As Possible:
You should try your best to finish your syllabus as soon as possible. The early completion of the syllabus will be an advantage that you will still have a lot of time left to re-read those studied topics.
Revision notes prove to be very helpful during exam time. You should make revision notes for each subject only then it will be beneficial. In the revision notes, you should write all those points which can come in the exam.
Every student has this problem, whatever they remember, they forget quickly. The biggest reason for this is that they do not read back the things they have read, once they have read it, they read it at the time of the exam itself.
At least you should solve the last three year papers, by this, you will get an idea of what kind of questions come and how much time it takes to solve them.
On the day of the exam, don't stress your mind at all and have full faith from the inside that the paper will go well. If there is such a topic that you have forgotten to read, then do not try to read it at all.
When you get the question paper, then take a look at those questions for 15 minutes and leave those questions which you do not know and try to do those that you know well first.